Interrupt 12h	Memory Size
(0:0048h)       get system memory 
return  AX      number of contiguous 1K RAM blocks 
note:	1) On some early PC models, the amount of memory returned by this 
	   function is controlled by the settings of the dip switches on the 
	   system board and may not reflect all the memory that is physically 
	   present.
	2) On the AT, the value returned is the amount of functional memory 
	   found during the power-on self-test, regardless of the memory size 
	   configuration information stored in CMOS RAM.
	3) The value returned does not reflect any extended memory (above the 
	   1 Mb boundary) that may be installed on 80286 or 80386 machines 
	   such as the AT or PS2 (models 50 and above)
	4) This is the same as the value at BIOS\Address -40:13